1. Field of the Invention
The present invention relates to an improved snatch block having a movable sideplate, a snatch block assembly and a method of using a snatch block to enable installation or removal of a rope.
2. State of the Art
A snatch block is a pulley-block that can be opened to receive a bight of a rope. Generally, a block refers to a pulley or a system of pulleys set in a casing. Conventionally, the casing is provided with a hook, eye, or strap, by which it may be attached to another structure. A pulley is a simple machine consisting essentially of a wheel with a grooved rim in which a pulled rope or cable can be run to change the direction of a force applied to the rope or cable to move a load. The wheel may be a sheave that rotates on a bearing. A sheave refers to a wheel or disk with a grooved rim.
Pulleys are used for various applications in many different activities, especially those activities employing ropes or cables. Pulleys may be used for outdoor recreational activities, such as rock climbing, mountaineering, caving, and mountain rescue work. However, pulleys are also employed in applications, such as in sailing and other marine applications, in urban and industrial rescue work, in safety restraints used in urban and industrial settings, in lifting and material handling in urban and industrial settings, in law enforcement, in tree climbing, and in military applications, among many others. The foregoing activities will be referred to herein generally as “rigging applications.”
FIG. 1 illustrates a conventional swing-sided pulley 100 as used with outdoor recreation activities. A first sideplate 10 pivots with respect to a second sideplate 20 about an axle 45. This provides access to a sheave 50 for inserting a bight of a rope (not shown). An opening 30 of the first sideplate 10 and an opening 35 of the second sideplate 20, when aligned, provide an attachment point for a carabiner, also known as a snap-link (not shown). Attaching a carabiner through the aligned openings 30, 35 prevents the first sideplate 10 from pivoting with respect to the second sideplate 20, and holds the rope in place between the first sideplate 10 and second sideplate 20. The swing-sided pulley 100 must be detached from the carabiner to insert or remove the bight of rope. Additionally, the swing-sided pulley 100 can only be attached to another structure in a single plane; that is, the sheave does not swivel with respect to the attachment point.
FIGS. 2A and 2B illustrate a snatch block assembly 15 for the lifting and material handling industry, described in U.S. Pat. No. 6,481,695, assigned to The Crosby Group, Inc. of Tulsa, Okla. The snatch block assembly 15 includes a fixed sideplate 12 and a swing sideplate 14. A nut 40 supports a swivel hook 42 from a trunnion 38. Support means 16 holds the fixed sideplates 12 and the swing sideplate 14 apart and supports a sheave member 18 over which a rope (not shown) will be threaded. When it is desired to replace a rope, bolt head 62 is turned to loosen threaded bolt 60 from the swing sideplate 14. Once the threads are free, the threaded bolt 60 may be moved axially in direction A until the swing sideplate 14 is free to swing to one side to permit the looping of the rope bight through the snatch block assembly 15. It is contemplated that a hammer may be used to loosen the bolt head 62. Turning a tight, threaded bolt may be cumbersome and awkward, slowing many rigging activities. In addition, this operation requires two hands of a user to place the snatch block assembly 15 in a configuration to receive a rope. Especially in a rescue situation, where speed is essential and the user may require one hand to ensure his or her own safety, this requirement may have potentially disastrous consequences.
In view of the foregoing, it appears that a snatch block having a quick and straightforward sideplate opening and closing mechanism is needed. A robust and simple, easily operable snatch block assembly having such a sideplate configuration and further configured to swivel with respect to an attachment point to another structure would also be useful.